I find myself at Jerry’s Home Improvement Store (much better than any Home Depot or Lowes) quite often these days, and there’s always a good chance of finding something worth a quick click. This tandem-axle Tacoma falls into that category, as these kind of conversions were once more common, but have become quite rare, especially on the later versions like this one.
The second rear axle is of course non-powered, often referred to as a “tag axle”, although that may imply that it can be raised when the load is light. It certainly is in this case, but there’s plenty of potential to put some serious weight on it, given the substantial rear overhang of this flatbed. Needs another axle back there, with steering.